Analysis by: Warren Adam Sto. Tomas
ALIASES:

Trojan horse Atros4.CFRU(AVG)

 PLATFORM:

Windows

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:
 INFORMATION EXPOSURE:

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

This backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

  TECHNICAL DETAILS

File Size: 2,418,667 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 13 Feb 2017

Arrival Details

This backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

Installation

This backdoor drops the following files:

  • %User Temp%\kd9bvI\x
  • %User Temp%\kd9bvI\um4e.dll
  • %User Temp%\kd9bvI\p
  • %System Root%\xKlydj7oohxKlydj7ooh\x
  • %System Root%\xKlydj7oohxKlydj7ooh\um4e.dll
  • %System Root%\xKlydj7oohxKlydj7ooh\xKlydj700h.exe
  • %Application Data%\Microsoft\xKlydj700h.exe
  • %Application Data%\Macromedia\xKlydj700h.exe

(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.. %System Root% is the Windows root folder, where it usually is C:\ on all Windows operating system versions.. %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

It drops and executes the following files:

  • %User Temp%\kd9bvI\mbTv10.exe

(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

It creates the following folders:

  • %User Temp%\kd9bvI
  • %System Root%\xKlydj7oohxKlydj7ooh
  • %Application Data%\Monitor\Files
  • %Application Data%\Monitor\Guard
  • %Application Data%\Monitor\Logs
  • %Application Data%\Monitor\Screenshots

(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.. %System Root% is the Windows root folder, where it usually is C:\ on all Windows operating system versions.. %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

Autostart Technique

This backdoor adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\RunOnce
xKlydj7ooh = %System Root%\xKlydj7oohxKlydj7ooh\xKlydj7ooh.exe

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Microsoft = %Application Data%\Microsoft\xKlydj7ooh.exe

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Driver = %Application Data%\Macromedia\xKlydj7ooh.exe

Other System Modifications

This backdoor adds the following registry entries:

HKEY_CURRENT_USER\Software
KuoNer2pXXZnM9wg1a5B0Q== = dPgewiSdtH+VEq1GhX6hDX6hd6YaUxx/eVYDM+cURPY=

HKEY_CURRENT_USER\Software
bhpRL2hxHV6cWLFgTdHlHQ== = c3QlcJNv2our3ZDXDJ4oog==

HKEY_CURRENT_USER\Software
PRC = 3776

HKEY_CURRENT_USER\Software
qiDSpS7Wo0a7UdJ6YI4KBA== = Qo9WQLcPiheyvdfJ14Lvx9Oi643cctbjiDGCZ4FnWOI=

HKEY_CURRENT_USER\Software
bhpRL2hxHV6cWLFgTdHlHQ== = Oa1sIB1v6WZEsi52YmSXsA==

HKEY_CURRENT_USER\Software
42nrW/VAiS5h8vwjeAqOTg== = XCACofi+cIbUenZFPQ5v6Q==

HKEY_CURRENT_USER\Software
aED8D/iKZFZoJ3KDSuB2lIAkDyEbDbIHDgfVnZKHSwo= = zzWHqQcRjg5gqbeHWxF1tQ==

HKEY_CURRENT_USER\Software
cZU98pShyk3+/E/NOT+pLc81h6kHEY4OYKm3h1sRdbU= = zzWHqQcRjg5gqbeHWxF1tQ==

HKEY_CURRENT_USER\Software
k8sGMC/2mz7wswpy3v7t/g== = UOEMWo5i1hm6aSEvqKPRtj42cPMNImLLAr27szeA45wf2ZRqlO56yWEftObalDll7Cq72WBvS7VRZjM6mDpAyXtxeeYkK1NFUX/ye/QS18x5DI95OCS7XA5zDUuYGvtzzzWHqQcRjg5gqbeHWxF1tQ==

HKEY_CURRENT_USER\Software
PTH = %Windows%\Microsoft.NET\Framework\v2.0.50727\regasm.exe

HKEY_CURRENT_USER\Software
MTX = 6248cd88890c2cbe2a0a9fa8f2e605fa3f62fc28

Other Details

This backdoor connects to the following possibly malicious URL:

  • {BLOCKED}.{BLOCKED}.217.22

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 13.218.07
FIRST VSAPI PATTERN DATE: 13 Feb 2017
VSAPI OPR PATTERN File: 13.219.00
VSAPI OPR PATTERN Date: 14 Feb 2017

Step 1

Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.

Step 2

Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

Delete this registry value

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\RunOnce
    • xKlydj7ooh = "%System Root%\xKlydj7oohxKlydj7ooh\xKlydj7ooh.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • Microsoft = "%Application Data%\Microsoft\xKlydj7ooh.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • Driver = "%Application Data%\Macromedia\xKlydj7ooh.exe"
  • In HKEY_CURRENT_USER\Software
    • KuoNer2pXXZnM9wg1a5B0Q = = = "dPgewiSdtH+VEq1GhX6hDX6hd6YaUxx/eVYDM+cURPY="
  • In HKEY_CURRENT_USER\Software
    • bhpRL2hxHV6cWLFgTdHlHQ = = = "c3QlcJNv2our3ZDXDJ4oog=="
  • In HKEY_CURRENT_USER\Software
    • PTH = "%Windows%\Microsoft.NET\Framework\v2.0.50727\regasm.exe"
  • In HKEY_CURRENT_USER\Software
    • MTX = "6248cd88890c2cbe2a0a9fa8f2e605fa3f62fc28"
  • In HKEY_CURRENT_USER\Software
    • PRC = "3776"
  • In HKEY_CURRENT_USER\Software
    • qiDSpS7Wo0a7UdJ6YI4KBA = = = "Qo9WQLcPiheyvdfJ14Lvx9Oi643cctbjiDGCZ4FnWOI="
  • In HKEY_CURRENT_USER\Software
    • bhpRL2hxHV6cWLFgTdHlHQ = = = "Oa1sIB1v6WZEsi52YmSXsA=="
  • In HKEY_CURRENT_USER\Software
    • 42nrW/VAiS5h8vwjeAqOTg = = = "XCACofi+cIbUenZFPQ5v6Q=="
  • In HKEY_CURRENT_USER\Software
    • aED8D/iKZFZoJ3KDSuB2lIAkDyEbDbIHDgfVnZKHSwo = = "zzWHqQcRjg5gqbeHWxF1tQ=="
  • In HKEY_CURRENT_USER\Software
    • cZU98pShyk3+/E/NOT+pLc81h6kHEY4OYKm3h1sRdbU = = "zzWHqQcRjg5gqbeHWxF1tQ=="
  • In HKEY_CURRENT_USER\Software
    • k8sGMC/2mz7wswpy3v7t/g = = = "UOEMWo5i1hm6aSEvqKPRtj42cPMNImLLAr27szeA45wf2ZRqlO56yWEftObalDll7Cq72WBvS7VRZjM6mDpAyXtxeeYkK1NFUX/ye/QS18x5DI95OCS7XA5zDUuYGvtzzzWHqQcRjg5gqbeHWxF1tQ=="

Step 5

Search and delete these folders

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %User Temp%\kd9bvI
  • %System Root%\xKlydj7oohxKlydj7ooh
  • %Application Data%\Monitor\Files
  • %Application Data%\Monitor\Guard
  • %Application Data%\Monitor\Logs
  • %Application Data%\Monitor\Screenshots

Step 6

Search and delete this file

[ Learn More ]
There may be some files that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the "More advanced options" option to include all hidden files and folders in the search result.
  • %Application Data%\Microsoft\xKlydj700h.exe
  • %Application Data%\Macromedia\xKlydj700h.exe

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_LUMINOSITY.AUSIKZ. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.


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